Sextus Pompey is the son of Pompey the Great, whom Julius Caesar had defeated just before the opening of Julius Caesar.
He leads a popular rebellion against the triumvirate, which is widespread enough that it forces Caesar and Antony to make a truce. He accepts a parley with the triumvirate and in the end agrees to their terms, and suggests that they feast together. When Menas suggests to him that they set sail and murder the triumvirate at table, he refuses out of honor, but wishes Menas had done so without telling him about it. Of all the rulers we see in the play, he is the only one who ever speaks of the good of the people.